1. Field of the Invention
The present invention relates to an olefin isomerization process employing a basic metal oxide catalyst and to the composition of the catalyst to improve its active life.
2. Description of the Related Art
There is a growing need for terminal (alpha) olefins such as 1-butene or 1-hexene. The commercial production of alpha olefins is usually accomplished by the isolation of the alpha olefin from a hydrocarbon stream containing a relatively high concentration of the 1-isomer. For example, 1-butene can be isolated from the C4 product of steam cracking. Steam cracking C4 streams contain not only the 1-butene stream but also 2-butene, isobutylene, butadiene and both normal and iso butanes. The 1-butene is isolated by first separating butadiene by extractive distillation or removing butadiene by hydrogenation. Isobutylene can be removed either by reaction (e.g. reaction with methanol to form MTBE), or by fractionation, with the remaining n-butenes being separated by distillation into a 1-butene overhead stream and a 2-butene bottom product. An alternate production method for alpha olefins involves the dimerization of ethylene to form 1-butene or the trimerization of ethylene to form 1-hexene. Other methods include molecular sieve adsorption of the linear olefins (used for low concentrations).
Another process for providing alpha olefins is catalytic isomerization from internal olefins, which accomplishes the shifting of the double bond in an olefin molecule from, for example, an internal position (2-butene) to a terminal position (1-butene). High temperatures favor the isomerization of internal olefin to the alpha olefin. However, high temperature tends to cause catalyst coking which shortens catalyst life. The duration of catalyst activity is a significant factor with respect to the economic viability of a process. The more often a process has to be interrupted for catalyst regeneration the more costly the process becomes. Hence, a method for maintaining peak catalyst activity over a longer period of time at high temperature is a significant advantage for olefin isomerization.